Spark-gap for roentgen-ray apparatus.



PATENTE'D APR. 12, 1904..

J. T. H. DEMPSTER. SPARK GAP FOR 'ROENTGEN RAY APPARATUS.

APPLIOATION I'ILBD JUNE 18, 1898.

2 SHEETS-SHEET 1.

N0 MODEL.

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WITNESSES.

No. 756,941. PATENTED APR. 12, 1904.

J. T. H. DEMPSTER. I

SPARK GAP FOR ROENTGEN RAY APPARATUS.

APPLICIATION FILED JUNE 18, 1898. no MODEL. 2 SHBETSQSHEET z.

WITNESSES. 'INVEN IJ @2155 f JobnT em ostev'.

m2. ucnms PEYER$ c0 uoraumcn, wAsnmsmu D c UNITED STATES Patented April 12, 1904.

PATENT OFFICE.

JOHN T. H. DEMPSTER, OF SOHENEOTADKNEW YORK, ASSIGNOR TO THE GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SPARK-GAP FOR ROENTGEN-RAY APPARATUS.

SPECIFICATION forming part of Letters Patent No. 756,941, dated April 12, 1904.

Application filed June 18, 1898.

To all whom, it natty concern:

Be it known that I, JOHN T. H. DEMPSTER, a subject of the Queen of Great Britain, residing at Schenectady, in the county of Schenectady and State of New York, have invented certain new and useful Improvements in Spark- Gaps for Roentgen-Ray Apparatus, of which consisting of two straight rods terminating in balls, is employed, the balls heat rapidly and a certain amount of metal becomes volatilized, so that the resistance of the spark-gap is materially reduced, and the surfaces of the balls become rough. Thus the gap requires constant adjustment and soon becomes unsatisfactory. To obviate this, an air-blast has been used for cooling the balls, both a fanblast and a blast produced by a chimney, and the balls have been made large; but in spite of these expedients it is difiicult to keep the terminals cool or to obtain suflicient draft. To avoid this diificulty, I use spark-gaps of ordinary form, but mounted upon a disk rapidly revolved by asmall electric motor. I have found the ordinary fan-motors suitable for this purpose, as the speed is high and the current consumption small. mount the terminals on a disk in the way suggested, preferably with collecting-rings, so that the circuit may remain unbroken except at the spark-gap, and with this arrangement, owing to the high speed of rotation, the draft is siifiicient to keep the terminals constantly coo In the accompanying drawings I show one embodiment of the invention.

Figure 1 is a side elevation of the device; Fig. 2, an end elevation looking to the left of Fig. l, and Fig. 3 a diagram of the circuits.

The apparatus shown in Fig. 1 consists ofa small motor I, having a projecting shaft B carrying a revolving spark-gap device. Upon ancing each other.

I therefore.

Serial No. 683,779- .(Nn model.)

the shaft are mounted two collars F and F, the collar F being fixedly secured to the shaft in some suitable manner, as by means of a pin 1, while the collar F is free to move longitudinally. Disks G G, preferably of insulating material, are secured, respectively, to the collars F F and upon their periphery carry balls H H and H H of conducting material. These balls constitute the terminals of spark-gaps and are arranged so that the balls of each pair are opposite each other. The balls on each disk are also arranged op .posite each other, thereby mechanically bal- In order to adjust the length of the spark-gaps, the disk Gr, carrying theballs H H, is arranged so as to slide back- Ward or' forward upon the shaft B In order to allow this longitudinal motion without at the same time permitting a displacement of the balls by relative rotation of the disks F F, I

I make use of a pin or pins P, fixed at one end to one of the disks-as, for example, the disk Gand at its other end closely engaging a hole in the other disk, Gr. Any other suitable mechanical device forpermitting longitudinal movement withoutrotation about the shaft may of course be employed, if desired. In order to move the sleeve F, together with the disk G and attached parts, backward or .for-

ward upon the shaft B while the apparatus is in motion, I make use of aforked lever O, pivotally mounted on the upper end of a post C. The forks of the lever carry pins 0, which engage a groove in a metallic collar E, fastened to the insulating-collar F. This collar E is made of metal in order to reduce friction electrical connections with the revolving apparatus are made bymeans of brushes K K, supported, respectively, upon posts of insulating material B B and bearing upon collector-rings D D, as will readily be seen.

Current passing into a brush K traverses the collector-ring D and the wire W to the ball Thence it jumps across the air-gap to the ball H passing then through the wire or other conductor W to the ball H", then across the air-gap to the ball H, and by wire W to the collector-ring D and out through the brush K,

Fig. 3 shows the circuits. In this figure T is a transformer across the secondary circuit of which is connected the condenser L. In circuit with the secondary is the primary of another transformer T both of the transformers, as is well understood, being step-up devices. In the circuit of the condenser and including the primary of the transformer T is the spark-gap device. In the secondary of the transformer T is the Crookes tube M, of a form now well known, especially adapted for alternating currents.

The operation of thedevice, while easily understood, is briefly as follows: Alternating current at moderate potential is supplied to the transformer 'I" and is stepped up as high as is convenient, so as to be suitable'for the condenser L. The transformer T further steps up the current to a potential proper for the operation of the Crookes tube M. The frequency in the second transformer is of course enormously high compared to that in the transformer T, being determined by the capacity, inductance, and resistance of the circuit, including the spark-gap device,in accordance with the principles of oscillating electric currents, the condenser being alternately charged and discharged. The path of the condenser discharge is through the primary of the transformer T collecting-brush K, collector-ring D, across the gap between the balls H H then by the lead from the ball H to H across the second spark-gap to the ball H, to the collector-ring D, brush'K, back to the condenser, the current oscillating through this path in the well-known way as the condenser is alternately charged and discharged. Since the balls continuously revolve at high speed, a draft of air is obtained suflicient to keep them cool during any ordinary run of the apparatus.

It will he understood that the electrical connection may be varied, so that my improved spark-gap is useful in various relations other than that described.

What I claim as new, and desire to secure by Letters Patent of the United States, is.

1. An arc-rupturing device comprising terminals between which the arc is formed and means for revolving said terminals.

2. A spark-gap apparatus comprising relatively adjustable terminals and means for revolving said terminals.

3. The combination of spark-gap terminals normally in fixed relation to each other, and

means for simultaneously moving said terminals through a fluid in a direction at an angle to a line between said terminals.

4. The combination of synchronously-moving spark-gap terminals and means for causing sparks to pass between said terminals.

5. The combination-of synchronously-moving spark-gap terminals, and means for adjus'ting the length of the spark-gap while the terminals are in motion.

6. The combination of spark-gap terminals with means for synchronously revolving said terminals.

'7. In-a spark-gap apparatus, the combination of a rotating disk, a pair of balls carried upon the disk, a second disk facing the first and also carrying a pair of balls, collector rings and brushes, with a connection from the collector-rings to one of each of the sets of balls and an electrical connection between the remaining balls.

8. The combination of a motor, a pair of disks driven thereby, and spark-gap terminals at opposite points upon the disks, so arranged as to mechanically balance the latter, with means for leading current to the disks.- v

9. The combination with spark-gap terminals, of means for moving the gap included between the terminals without changing 'the relation between the terminals and the included gap, to keep the terminals cool.

- In witness whereof I have hereunto set my hand this 14th day of June, 1898.

JOHN T. H. DEMPSTER.

Witnesses:

B. B. HULL, M. H. EMERSON. 

